Printable organometallic perovskite enables large-area, low-dose X-ray imaging.

Medical X-ray imaging procedures require digital flat detectors operating at low doses to reduce radiation health risks. Solution-processed organic-inorganic hybrid perovskites have characteristics that make them good candidates for the photoconductive layer of such sensitive detectors. However, such detectors have not yet been built on thin-film transistor arrays because it has been difficult to prepare thick perovskite films (more than a few hundred micrometres) over large areas (a detector is typically 50 centimetres by 50 centimetres). We report here an all-solution-based (in contrast to conventional vacuum processing) synthetic route to producing printable polycrystalline perovskites with sharply faceted large grains having morphologies and optoelectronic properties comparable to those of single crystals. High sensitivities of up to 11 microcoulombs per air KERMA of milligray per square centimetre (µC mGyair-1 cm-2) are achieved under irradiation with a 100-kilovolt bremsstrahlung source, which are at least one order of magnitude higher than the sensitivities achieved with currently used amorphous selenium or thallium-doped cesium iodide detectors. We demonstrate X-ray imaging in a conventional thin-film transistor substrate by embedding an 830-micrometre-thick perovskite film and an additional two interlayers of polymer/perovskite composites to provide conformal interfaces between perovskite films and electrodes that control dark currents and temporal charge carrier transportation. Such an all-solution-based perovskite detector could enable low-dose X-ray imaging, and could also be used in photoconductive devices for radiation imaging, sensing and energy harvesting.

Asymmetric carrier transport in flexible interface-type memristor enables artificial synapses with sub-femtojoule energy consumption.

Flexible and transparent artificial synapses with extremely low energy consumption have potential for use in brain-like neuromorphic electronics. However, most of the transparent materials for flexible memristive artificial synapses were reported to show picojoule-scale high energy consumption with kiloohm-scale low resistance, which limits the scalability for parallel operation. Here, we report on a flexible memristive artificial synapse based on Cs3Cu2I5 with energy consumption as low as 10.48 aJ (= 10.48 × 10-18 J) µm-2 and resistance as high as 243 MΩ for writing pulses. Interface-type resistive switching at the Schottky junction between p-type Cu3Cs2I5 and Au is verified, where migration of iodide vacancies and asymmetric carrier transport owing to the effective hole mass is three times heavier than effective electron mass are found to play critical roles in controlling the conductance, leading to high resistance. There was little difference in synaptic weight updates with high linearity and 250 states before and after bending the flexible device. Moreover, the MNIST-based recognition rate of over 90% is maintained upon bending, indicative of a promising candidate for highly efficient flexible artificial synapses.

Interplay between electrochemical reactions and mechanical responses in silicon-graphite anodes and its impact on degradation.

Durability of high-energy throughput batteries is a prerequisite for electric vehicles to penetrate the market. Despite remarkable progresses in silicon anodes with high energy densities, rapid capacity fading of full cells with silicon-graphite anodes limits their use. In this work, we unveil degradation mechanisms such as Li+ crosstalk between silicon and graphite, consequent Li+ accumulation in silicon, and capacity depression of graphite due to silicon expansion. The active material properties, i.e. silicon particle size and graphite hardness, are then modified based on these results to reduce Li+ accumulation in silicon and the subsequent degradation of the active materials in the anode. Finally, the cycling performance is tailored by designing electrodes to regulate Li+ crosstalk. The resultant full cell with an areal capacity of 6 mAh cm-2 has a cycle life of >750 cycles the volumetric energy density of 800 Wh L-1 in a commercial cell format.

Novel Flexible Transparent Conductive Films with Enhanced Chemical and Electromechanical Sustainability: TiO2 Nanosheet-Ag Nanowire Hybrid.

Flexible transparent conductive films (TCFs) of TiO2 nanosheet (TiO2 NS) and silver nanowire (Ag NW) network hybrid were prepared through a simple and scalable solution-based process. The as-formed TiO2 NS-Ag NW hybrid TCF shows a high optical transmittance (TT: 97% (90.2% including plastic substrate)) and low sheet resistance (Rs: 40 Ω/sq). In addition, the TiO2 NS-Ag NW hybrid TCF exhibits a long-time chemical/aging and electromechanical stability. As for the chemical/aging stability, the hybrid TCF of Ag NW and TiO2 NS reveals a retained initial conductivity (ΔRs/Rs < 1%) under ambient oxidant gas over a month, superior to that of bare Ag NW (ΔRs/Rs > 4000%) or RuO2 NS-Ag NW hybrid (ΔRs/Rs > 200%). As corroborated by the density functional theory simulation, the superb chemical stability of TiO2 NS-Ag NW hybrid is attributable to the unique role of TiO2 NS as a barrier, which prevents Ag NW's chemical corrosion via the attenuated adsorption of sulfidation molecules (H2S) on TiO2 NS. With respect to the electromechanical stability, in contrast to Ag NWs (ΔR/R0 ∼ 152.9%), our hybrid TCF shows a limited increment of fractional resistivity (ΔR/R0 ∼ 14.4%) after 200 000 cycles of the 1R bending test (strain: 6.7%) owing to mechanically welded Ag NW networks by TiO2 NS. Overall, our unique hybrid of TiO2 NS and Ag NW exhibits excellent electrical/optical properties and reliable chemical/electromechanical stabilities.

Metallic conduction induced by direct anion site doping in layered SnSe2.

The emergence of metallic conduction in layered dichalcogenide semiconductor materials by chemical doping is one of key issues for two-dimensional (2D) materials engineering. At present, doping methods for layered dichalcogenide materials have been limited to an ion intercalation between layer units or electrostatic carrier doping by electrical bias owing to the absence of appropriate substitutional dopant for increasing the carrier concentration. Here, we report the occurrence of metallic conduction in the layered dichalcogenide of SnSe2 by the direct Se-site doping with Cl as a shallow electron donor. The total carrier concentration up to ~10(20) cm(-3) is achieved by Cl substitutional doping, resulting in the improved conductivity value of ~170 S · cm(-1) from ~1.7 S · cm(-1) for non-doped SnSe2. When the carrier concentration exceeds ~10(19) cm(-3), the conduction mechanism is changed from hopping to degenerate conduction, exhibiting metal-insulator transition behavior. Detailed band structure calculation reveals that the hybridized s-p orbital from Sn 5s and Se 4p states is responsible for the degenerate metallic conduction in electron-doped SnSe2.

Capillary flow of amorphous metal for high performance electrode.

Metallic glass (MG) assists electrical contact of screen-printed silver electrodes and leads to comparable electrode performance to that of electroplated electrodes. For high electrode performance, MG needs to be infiltrated into nanometer-scale cavities between Ag particles and reacts with them. Here, we show that the MG in the supercooled state can fill the gap between Ag particles within a remarkably short time due to capillary effect. The flow behavior of the MG is revealed by computational fluid dynamics and density funtional theory simulation. Also, we suggest the formation mechanism of the Ag electrodes, and demonstrate the criteria of MG for higher electrode performance. Consequently, when Al85Ni5Y8Co2 MG is added in the Ag electrodes, cell efficiency is enhanced up to 20.30% which is the highest efficiency reported so far for screen-printed interdigitated back contact solar cells. These results show the possibility for the replacement of electroplating process to screen-printing process.